1. Field of the Invention
The present invention relates to a keyboard device suitable for use in a notebook type personal computer.
2. Description of the Related Art
As shown in FIGS. 9 and 10, a keyboard device K used in a conventional notebook type personal computer has a support plate 21 constituted by a flat metallic plate, with a switch member 22 being mounted on the support plate 21.
The switch member 22 has a sheet 23 for fixed contacts formed by a filmy insulator, a sheet 24 for a spacer formed by filmy insulator on the sheet 23, and a sheet 25 for movable contacts formed by a filmy insulator on the sheet 24. These sheets are laminated and bonded together integrally.
The sheets 23 for fixed contacts and the sheet 25 for movable contacts are each provided with a large number of contacts (not shown) formed of silver for example, the contacts on both sheets being in an opposed relation vertically at the position of a hole 24a formed in the sheet 24 for a spacer, to constitute the switch member 22.
The keyboard device K is provided with a holding member 26 formed on the switch member 22 by molding of a synthetic resin, a plurality of link members 27 mounted to the holding member 26 and each comprising two support pieces crossing each other and adapted to fall down and thereby movable vertically, a plurality of key-tops 28 secured to the link members 27, and dome members 29 formed of rubber whose upper portions are opposed to the key-tops 28 and whose lower portions are secured to the holding member 26.
The keyboard device K of such a construction operates in the following manner. When a key-top 28 is depressed, the associated link member 27 falls down and the associated dome member 29 is pushed by the key-top 28 and is thereby deformed and inverted. Wit dome member 29, the sheet 25 for movable contacts is pressed and comes into contact with the associated contact on the sheet 23 for fixed contacts. In this way there is made switch-over from one contact to another.
When the pressure on the key-top 28 is released, the sheet 25 for movable contacts leaves the sheet 23 for fixed contacts to make switch-over of contacts. At the same time, the dome member 29 reverts to its original state by virtue of its own elasticity, and with the dome member 29, both key-top 28 and link member 27 also revert to their original states.
As shown in FIGS. 9 and 10, the keyboard device K of the above construction is mounted within a box-shaped case 31 provided with a lid 30 which can be opened and closed, to constitute a personal computer P.
In the personal computer P, a printed circuit board 32 with constituents of various control circuits being connected by wiring is housed within the case 31.
On the printed circuit board 32 is disposed an IC component 33 which generates a large quantity of heat, and the support plate 21 of the keyboard K is positioned on the IC component 33.
The spacing between the IC component 33 and the support plate 21 is very small and both are very close to each other, nearly in contact with each other, to meet the recent demand for a thinner structure of the personal computer P.
Consequently, when the personal computer P is in use, the IC component 33 generates heat, so that the support plate 21 as a metallic plate positioned near the IC component 33 is heated. Consequently, the sheets 23 and 25 for fixed and movable contacts of the switch member 22 positioned on the thus-heated support member 21 are affected.
Thus, the conventional keyboard device K involves the problem that since the switch member 22 is mounted on the support plate 21 located near the IC component 33 which generates heat, the heat generated from the IC component 33 is transmitted through the support plate 21 to the sheets 23 and 25 of the switch member 22, resulting in the sheets 23 and 25 being elongated and causing a contact defect.
There also is a problem such that the generation of heat from the IC component 33 causes a performance defect of the IC component, which may lead to malfunction of the personal computer P.